Cooking creates undesirable by-products, such as heat, steam, grease and odors. These cooking by-products pollute the air in a home or commercial environment if they are not safely removed. These cooking by-products are irritating, harmful and potentially hazardous. Accordingly, a multitude of ventilation systems have been developed to draw the cooking by-products away from the immediate vicinity of the cooking area and to expel this contaminated air to an external environment through an exhaust duct.
The heat generated from cooking expands the air and rises, carrying with it the cooking by-products. These typical ventilation systems use a hood placed above the cooking area to capture the by-products prior to removal by a blower system. The hood is like a small room wherein too much air flow is as harmful as too little. If too much air is removed from a well insulated home a negative pressure results rendering the ventilation system ineffective unless expensive make-up air is introduced. As a result the blower system should be sized based on the expected usage of the cooking area. For example, a barbecue grill, or wok should be measured at full value because they are most often at the high setting. Multiple burners, however, are rarely all turned to the high setting at any one time and should be discounted. As a result blower systems are typically controlled by switches which allow the user to select the fan speed from a couple of choices.
But if the selected fan speed of the blower system is too low, the fan will under-exhaust allowing heat and/or cooking by-products to escape from the hood and into the kitchen and, perhaps, the rest of the facility. On the other hand, if the fan speed of the blower system is too high, the fan will over-exhaust allowing too much air to be expelled while the motor is consuming energy unnecessarily. As a result, the air heated or cooled by the air conditioning system of the building is also exhausted to the outside, causing the thermostat of the air conditioner to run the air conditioning system to replace the exhausted air. This resulting inefficiency increases the owner's utility bills and needlessly wastes energy. This situation may also shorten the life of the exhaust fan motor.
Numerous attempts have been made in the past to overcome these difficulties, but they generally add complexity and expense to the ventilation systems. One approach has been to install a fresh air blower with an exhaust vent located near the cooking area, so that outside air is blown into the cooking area to be exhausted along with the cooking by-products instead of the building's air conditioning. Other systems automatically operate the ventilation system in response to detecting smoke or particles emitted from the cooking area. Another suggested method was to vary the speed of the blower system in proportion to the temperature of the air above the cooking units or the level of cooking by-products in the air flow path.
These devices, however, are not entirely adequate to overcome these problems, since they often involve complicated and expensive circuitry and detection devices. Moreover, these detection devices are normally mounted within the vent and are susceptible to damage from the accumulation of grease and small grease fires which sometimes occur within the cooking area. In addition, these detection devices require frequent maintenance to prevent the system from operating improperly or being rendered inoperative due to the accumulation of grease.
Some ventilation systems have attempted to solve the problem of grease accumulation by including devices to wash the chamber and the exhaust duct periodically. In addition, to conform with known safety rules, conventional ventilation systems usually include a safety mechanism designed to prevent the propagation of fires through the exhaust ducts linking the exhaust hood to an external environment. One common safety mechanism consists of a damper that is automatically closed when abnormally elevated temperatures are detected in or near the exhaust duct. A disadvantage of using a damper or blower system cut-off is the fact that the smoke generated by an eventual fire may not be exhausted.